Early ontogenetic shells of Recent and fossil Scaphopoda Theo S. Engeser, Frank Riedel & Klaus Bandel Engeser, T.S., F. Riedel & Κ. Bandel. Early ontogenetic shells of Recent and fossil Scaphopoda. — Scripta Geol., Spec. Issue 2: 83­100, 4 figs., 3 pls, Leiden, December 1993. Theo S. Engeser, Frank Riedel, Klaus Bandel, Geologisch­Paläontologisches Institut und Museum, Universität Hamburg, Bundesstraße 55, D­2000 Hamburg 13, Germany Key words: Scaphopoda, larval shell, early juvenile shell, new genus, Jurassic, Tertiary, Recent. The formation of the early ontogenetic shell of Scaphopoda is reviewed. In the few known cases the embryos hatch in the gastrula stage and rapidly develop into a lecithotrophic Trochophora­like larva. Our material indicates that there might be a planktotrophic larva in some species. The clasp­like shell is formed in the larval stage (e.g. Antalis tarentina Lamarck, 1818). It later fuses into a tube and mineral­ ises during metamorphosis. Immediately after the metamorphosis the shell increases at the anterior end (early teleoconch) and posterior end (fumarium). During further growth, the fumarium, the larval shell and finally parts of the juvenile shell are gradually resorbed. We describe several specimens with preserved protoconchs from different stratigraphie units: the Early Jurassic, the Middle Jurassic, the Palaeocene, the Oligocene, the Miocene, the Pliocene, and a Recent example. Some specimens with preserved larval shells illustrated in the literature have not been recognised as such. They are briefly reviewed. At least two different types of protoconchs (and some modifications) can be recognised within the Scaphopoda. The new data are not yet sufficient to arrange larger systematic units using the different protoconch types. It is evident, however, that in fossil Scaphopoda species with convergent adult shells can only be discovered by a synthesis of larval, juvenile and adult shell characters (shape, size, sculpture). A new genus and species, Suevidontus jaegeri gen. et sp. nov. from the late Middle Jurassic of southern Germany is introduced. The family attribution of the new genus is uncertain. Contents Introduction 83 Termini 83 Material and methods 85 General account of the early ontogeny of Scaphopoda 85 Descriptions 86 Comparison with other specimens 96 Discussion 98 Acknowledgements 99 References 99 Introduction Termini Teleoconch includes the juvenile and/or the adult shell. Protoconch is used as a synonym for the larval shell prior to metamorphosis. As far as known no embryonic 84 Engeser et al., Early ontogenetic shells of Scaphopoda. Scripta Geol, Spec. Issue 2 (1993) shell is built during the ontogeny of the Scaphopoda. Since there exist no detailed descriptions of the protoconch of scaphopods we introduce several new termini (see also Fig. 1). The larval shell looks like a clasp before it becomes fused ventrally. The seam of adhesion of the two lateral parts of the protoconch is called suture. The suture can be well developed but also very indistinct. The shell of the suture area is often wrinkled. The lateral parts of the larval shell are mostly 'inflated' and somewhat resemble human cheeks. We therefore called them genae (sing, gena) from the Latin word for cheek. The genae are most pronounced when the suture is relatively deepened in regard to the surface. The posterior opening can be very narrow or of a moderate diameter. It may be surrounded by a low wall or by a pipe. This pipe looks like a chimney and we there• fore introduce the Latin word fumarium for it. We do not know whether a fumarium is always present during a certain ontogenetic phase. The fumarium is not a part of the protoconch since it is formed after metamorphosis (see below). The anterior part of one of the larval shell types shows weak to strong circular annulations or undulations. We generally call these structures annulations because without destroying the specimens one cannot decide whether the ornamentation is restricted to the outer part of the shell or reaches the inner surface. The anterior protoconch often shows a constriction which is more or less distinct. It does not represent the very end of the larval shell which is marked by the onset of strong growth lines, shell irregularities and/or e.g. the onset of longitudinal ribs. The surface of the larval shell may be covered by longitudinal lirae. Single lirae may bifurcate at the posterior end and can vary in strength as well as distance from each other. Fig. 1. Schematical drawing of a scaphopod protoconch with parts of the early teleoconch. Engeser et al., Early ontogenetic shells of Scaphopoda. Scripta Geol., Spec. Issue 2 (1993) 85 Material and methods The Recent Antalis tarentina and another juvenile dentaliid shells (not specifically identified) were collected off the coast of Banyuls­sur­Mer (southern France). The Pliocene scaphopod Entalinopsis sp. comes from Le Puget­sur­Argens (southern France), the Middle Miocene samples were borrowed from the Museum of Natural History in Vienna and had been collected at Baden (near Vienna). Samples of the Late Oligo­ cène 'Kasseler Meeressande' (Glimmerode, Germany) contained several juvenile speci­ mens. The Palaeocene material was collected at Matthew's Landing (Alabama, USA). Jurassic specimens come from the Dogger beta (Late Aalenian) of Hambühren (Lower Saxony, Germany), the Dogger zeta (Middle Callovian) of Plettenberg near Stuttgart (southern Germany) and from erratic boulders (Middle Liassic) found at Hoisbüttel (northern Germany). The fossil material was processed like usual micro samples using H202. Several samples were again treated with tensides (Rewoquat) to remove remaining clay chips. The specimens were sorted from the dried residue, mounted on stubs and coated with gold. They were investigated and photographed with the aid of a CamScan scanning electron microscope. General account of the early ontogeny of Scaphopoda The early ontogeny of scaphopods is poorly known. Only 7 Recent species out of probably more than 500 have been investigated in this regard (McFadien­Carter, 1979; Lindberg, 1985). In particular the formation and mineralisation of the proto­ conch are almost unknown. Modern developmental studies mainly concentrate on the early embryogeny (e.g. Verdonk & van den Biggelaar, 1983). We give a brief general account of the early ontogeny based on Recent Antalis tarentina (Lamarck, 1818) and A. vulgaris (da Costa, 1778) from the Mediterranean and the Channel (Palmer, 1987). Different stages of shell construction described from fossil specimens (see below) are used as additional data. Female and male scaphopods release mature eggs and sperms through their pos­ terior shell opening into the open sea where fertilization takes place. According to Lindberg (1985) egg sizes in scaphopods vary between 60 μιη and 200 μιη. Usually the eggs contain a comparably large amount of yolk. In Antalis vulgaris (da Costa, 1778) the embryos hatch as gastrulae a few hours after fertilization and rapidly devel­ op into Trochophora­like larvae with lecithotrophic development (Lacaze­Duthiers, 1856­58). The protoconchs of some species indicate that there might be planktotroph­ ic development as well (see Descriptions and Discussion). Kowalevsky (1883) noted the differentiation of the shell gland of Antalis aff. taren­ tina (Lamarck, 1818) during the late gastrula stage. The formation of the first organic shell takes place during the early 'Trochophora' stage (Lacaze­Duthiers, 1856­58). Further construction leads to a clasp­like shell (Bandel, 1982). After 4­5 days in the plankton the larva metamorphoses and becomes benthonic (Lacaze­Duthiers, 1856­ 58). During metamorphosis the mantle margins and the still organic shell ventrally fuse into a tube. Subsequently, the shell is mineralised. The fumarium (in Antalis tarentina) forms immediately after metamorphosis. With further growth the larval 86 Engeser et al., Early ontogenetic shells of Scaphopoda. Scripta Geol, Spec. Issue 2 (1993) shell and later apical parts of the teleoconch are completely resorbed. This process may begin at a shell length of c. 1 mm. Descriptions Antalis tarentina (Lamarck, 1818) (PL 1, figs. 1­2) Recent, Mediterranean. The larval shell of this specimen (PL 1, fig. 1; compare Bandel, 1982) is 370 μιη long and has a diameter of 165 μιη. The fumarium has a length of 100 μιη and shows distinct growth lines. The posterior opening is oval and orientated obliquely with regard to the long axis of the larval shell. Thus, the ventral part of the fumarium is shorter than the dorsal one. The first 280 μιη of the protoconch are almost smooth whereas the remaining 90 μιτι show growth lines. No constriction is present. The periostracum shows punctation (PL 1, fig. 2). The first 100 urn of the early teleoconch have no ornamentation except for growth lines. The following shell bears c. 15 longitudinal ribs which increase in number, become fainter and finally disappear during the ontogeny The final (late ontogenetic) teleo­ conch bears longitudinal ribs on its older apical half and is free of ribs on the young­ er apertural half. Apical and apertural cross sections are circular. Entalinopsis sp. (PL 1, figs. 3­4) Early Pliocene (Zanclian), Le Puget­sur­Argens (France) This specimen is a juvenile and could therefore not be identified specifically. The six prominent primary ridges and the flat, slightly concave, areas between them are characteristic for the genus Entalinopsis Habe, 1957. Several species, subspecies and varieties are known from the Pliocene (group of Dentalium sexangulum Schröter, 1784; see Sacco, 1897; Bellini, 1909; Cerulli­Irelli, 1910; Caprotti, 1979). Plate 1. Fig. 1. Antalis tarentina (Lamarck, 1818), Recent, Mediterranean, juvenile shell shortly after metamor­ phosis. Scale = 400 μπ\. Fig. 2. Antalis tarentina (Lamarck, 1818), Recent, Mediterranean, same specimen as fig. 1, magnified larval shell, showing periostracum punctation. Scale = 20 μιη. Fig. 3. Entalinopsis (?) sp., Pliocene of Le Puget­sur­Argens, France, juvenile shell. Scale = 1 mm. Fig. 4. Entalinopsis (?) sp., Pliocene of Le Puget­sur­Argens, France, same specimen as fig. 3, protoconch.